In display systems deriving signals from cathode ray tube signal generators of either the monoscope or the photosensitive camera tube type, targets have been used in which solid state junctions have been formed in materials such as semiconductors by diffusing a junction into the semiconductor. However, this process is often subject to imperfections in the target since in general junctions are formed in slices of semiconductor material grown from a melt and local areas of the slice will have crystal lattice imperfections. Hence during the diffusion process areas of the target where the imperfections occur will have junction regions which operate to produce a lower signal or no signal while regions having little or no such imperfections will produce a higher signal and as a result visually discernable differences can occur when signals generated by such devices are displayed on a display surface such as a cathode ray tube. While it is possible to obtain targets where the size and number of imperfections is small enough to produce usable devices, the resultant increase in production costs makes signal generators using such targets economically unfeasable for many applications.